1. Field of the Invention
This invention relates to a plate making device for a general light printer, particularly to an offset printer, which facilitates making a printing plate and makes it feasible to repeatedly recycle and reuse the printing plate. This invention further relates to a printer and a printing system using such a plate making device.
2. Description of the Related Art
Offset printing has been in wide use among others due to its simple plate making step. This printing method is based on immiscibility of oil and water, and oil material, i.e., ink, and fountain solution are selectively held in an imaged region and a non-imaged region, respectively. When a printing medium is brought into contact with the surface of the plate directly or by way of an intermediate member called a blanket, the ink on the imaged region is transferred to the printing medium, whereby printing is effected.
A prevailing method of the offset printing involves use of a PS plate which comprises an aluminum base plate and a diazo photosensitive layer formed on the base plate. In the PS plate, the surface of the aluminum base plate is subjected to sand dressing, anodizing and other steps in order to enhance ink receptivity of the imaged region and ink repellency of the non-imaged region, to increase durability against repeated printing and to increase fineness of the printing plate. An image to be printed is formed on the surface of the PS plate thus processed. Accordingly, the offset printing is excellent in durability against repeated printing and fineness in the printing plate as well as simplicity.
However as the printed matter spreads wider, there arises a demand for simpler offset printing and there have been proposed various simple printers.
The typical examples of such simple printers include printers in which a printing plate is made by use of a silver salt diffusion transfer method such as a "Copyrapid" offset printer available from "Agfa-Gevaer", a printer disclosed for instance in Japanese Unexamined Patent Publication No. 7(1995)-56351, and the like. In such printers, a transfer image can be formed in one step on a plate material and since the transfer image is lipophilic, the plate can be used as a printing plate as it is. However since even such printers require a diffusion transfer development step using an alkali developing solution, there is a demand for further simpler printer which requires no developing step by a developing solution.
Thus there have been made attempts to realize a simple printing plate which requires no developing step by an alkali developing solution. In the field of the simple printing plate, which is called a non-processed printing plate since it omits necessity of a developing step, there have been proposed various techniques primarily based on one of principles of (1) forming an image by recording an image on the surface of a plate material by image-wise exposure and thermally decomposing the exposed portion of the plate material, (2) forming an image by rendering lipophilic the exposed portion of the plate material in image-wise exposure by heat mode curing, (3) forming an image by rendering lipophilic the exposed portion of the plate material in image-wise exposure by light mode curing, (4) forming an image by modification of the surface of a plate material through decomposition by light, and (5) forming an image by heat mode melt transfer of an imaged portion.
The aforesaid simple offset printers are disclosed, for instance, in U.S. Pat. Nos. 3,506,779; 3,549,733; 3,574,657; 3,739,033; 3,832,948; 3,945,318; 3,962,513; 3,964,389; 4,034,183; 4,081,572; 4,693,958; 4,731,317; 5,238,778; 5,353,705; 5,385,092; and 5,395,729 and EP No. 1068.
Notwithstanding their advantage that they use no developing solution in making a printing plate, the aforesaid printers have one or more of the following drawbacks and are practically unsatisfactory. An unsatisfactory difference between the lipophilic region and the hydrophilic region, which results in poor quality of a printed image, poor resolution, which results in difficulty in obtaining a sharp printed image, an insufficient mechanical strength of the surface of a printed image to such an extent that the surface of the printed image is apt to be scratched, which requires provision of protective film or the like and deteriorates simplicity of the printer, and an insufficient durability against printing for a long time. Thus a strong demand for a printing plate which can be easily made and has various properties required in printing is not satisfied yet.
As a method of making a non-processed printing plate, there has been disclosed in Japanese Unexamined Patent Publication No. 9(1997)-169098 a method which utilizes a phenomenon that zirconia ceramic is rendered hydrophilic by exposure to light. However zirconia is insufficient in photosensitivity and cannot be sufficiently rendered hydrophilic from its hydrophobic (lipophilic) state. Accordingly the approach is disadvantageous in that the imaged region and the non-imaged region are not sufficiently distinguishable from each other.
Further it will be advantageous from the viewpoint of reduction in both cost and waste if a used printing plate can be easily recycled and reused. Simplicity of recycle operation is very important in recycle and reuse of printing plates, and it has been a very difficult problem to simplify the recycle operation. Accordingly there has been little disclosure on a method of overcoming this problem except Japanese Unexamined Patent Publication No. 9(1997)-169098 where the recycle operation is mentioned only on a zirconia ceramic plate material.